The manufacture of vinyl-4-cyclohexene (hereinafter called VCH) has been the object of substantial research for a long period of time. VCH is a material of prime interest because it can be easily dehydrogenated to form styrene and can also be used for the preparation of polycarboxylic acids as described in the French Pat. No. 2,218,314 by the Societe Nationale Des Petroles D'Aquitaine.
The manufacture of cyclooctadiene (hereinafter called COD) from butadiene has equally been the object of substantial research. COD is used as a starting material for the production of Nylon-8, suberic acid, succinic acid, and the derivatives of bicyclo[3.3.0] octadiene.
It has been known for some time that the specific dimerization of butadiene to VCH is possible by thermal means but this procedure requires a high temperature and the dimerization is slow. Additionally, a simultaneous polymerization occurs and competes with the desired Diels-Alder reaction.
Utilization of catalysts have been recommended to improve the speed of the butadiene dimerization. Catalyst systems which associate nickel, iron or manganese salts or complexes with coordinates of amines or phosphorus and with reductive compounds, in particular, organoaluminum compounds, convert butadiene into a mixture in which VCH is not the principal product.
In British Pat. No. 1,085,875 and 1,148,177, certain catalysts containing a metal such as iron, ruthenium or cobalt, a nitrosyl coordinate, a carbonyl coordinate and, in instances, trihaptoallyl, are taught to permit the manufacture of VCH in a selective manner from butadiene. In these patents, the use of iron dinitrosyl carbonyl, cobalt dinitrosyl dicarbonyl and iron trihaptoallyl-dicarbonyl nitrosyl are recommended. However, these catalytic systems have a number of disadvantages. Their preparation requires two reaction steps starting from the metal carbonyl and they have the major disadvantage of being volatile and being very toxic. When these catalysts are used, dimerization temperatures of at least 100.degree. C. are required which cause a rapid deactivation of the catalysts. Additionally, a substantially long induction period is also required which diminishes the yield achieved.
French Pat. No. 1,502,141 and 1,535,936 describe catalytic systems which have the advantage of dimerizing butadiene starting at lower temperatures. The former patent uses a catalyst constituted of a dinitrosyl iron halide associated with a donor compound and a reducer and the latter uses a dihalo bis(.pi. -allyl dinitrosyl iron) tin or germanium catalyst. U.S. Pat. No. 3,655,793 recommends the use of dinitrosyl iron halide in association with an organoaluminum compound with or without halogen.
All of the foregoing processes necessitate either the use of transition metal compounds requiring a multi-step preparation, or the use of expensive reductive compounds, which constitute further unfavorable aspects in the industrial interest in such catalytic systems.
In copending patent applications Ser. Nos. 404,888 and 404,889, filed on Oct. 10, 1973, owned by Societe Union Chimique Elf-Aquitaine and The Institut Francais du Petrole des Carburants et Lubrifiants, there is described improvements in the systems with two components. Such improvements principally consist in the ease of preparation of the two components in the absence of expensive reducing compounds and an optimum of activity with easily controllable temperatures of 40.degree.-60.degree. C. Those catalytic compositions allow the manufacture of VCH in a practically quantitative yield starting from pure butadiene, and in certain cases, even when starting with impure butadiene such as is present in the C.sub.4 fraction of vapor cracked petroleum fractions.
The present invention has the object of providing a new catalytic composition which overcomes the disadvantages of prior catalytic systems and some of the best results are obtained with catalysts whose components are easily obtained and inexpensive industrial products. This and other objects of the invention will become apparent to those skilled in the art from the following detailed description.